Agents that damage DNA reduce viability and can be mutagenic and carcinogenic. The long-term goals of this project are to understand cellular responses to DNA damage. In bacteria, the RecA protein controls the synthesis of enzymes that repair DNA and also directly participates in several repair pathways. To study the synthesis of RecA, mutants from a collection that affect its expression will be analyzed. To study the action of RecA, mutants that alter important sites in the protein will be studied. The possibility that some of the functions of RecA require its export from the cytoplasm will be studied with protein fusions to alkaline phosphatase. The relation of the amount of RecA in the cell to its activities will be determined using a hybrid gene in which RecA is made using the lac promoter. Changes in intracellular metabolism will also be studied by following the expression of cea, the gene for colicin E1, which is controlled by RecA, catabolite repression, anaerobiosis, nutrient deprivation, and DNA supercoiling. DNA rearrangements that result from recombination between repeated sequences will also be analyzed after DNA damaging treatments to determine if there may be constraints on recombination to maintain proper chromosome structure.